A colloidal silica is a dispersion of silica fine particles in media such as water etc., and are used not only as a property-improving agent in the fields of papers, fibers, steel, and the like, but also as a polishing material for electronic materials, such as semiconductor wafers, etc.
Mainly, two methods, i.e., a water glass method and an alkoxide method, have been known as production methods of a colloidal silica.
The water glass method is a method for growing particles by subjecting a sodium silicate to an ion exchange so as to prepare active silicic acid, and adding, with heating, the obtained active silicic acid to a seed particle-containing aqueous solution, in which the pH was adjusted with NaOH (Patent Document 1). According to this method, particles with a relatively dense structure can be obtained.
The alkoxide method, otherwise known as the Stöber method, comprises subjecting an alkyl silicate (tetraalkoxysilane) to hydrolyzation and condensation in the presence of a basic catalyst to grow particles, thereby producing silica particles. This method enables the preparation of colloidal particles having particle sizes ranging from nano- to microscale. For example, Patent Document 2 suggests a method for producing a cocoon-shaped colloidal silica, comprising adding methyl silicate (tetramethoxysilane) or a mixture of methyl silicate and methanol dropwise to a mixed solvent comprising water, methanol and ammonia, or to a mixed solvent comprising ammonia and ammonium salt under stirring for 10 to 40 minutes so as to allow the methyl silicate to react with water; and thereby producing a colloidal silica having a minor axis diameter of 10 to 200 nm and a major-axis/minor-axis ratio of 1.4 to 2.2. Further, Patent Document 3 discloses a method for producing a cocoon-shaped colloidal silica, comprising hydrolyzing a tetramethoxysilane tetramer while adding the tetramethoxysilane tetramer dropwise to a mixed liquid comprising methanol, water and ammonia.
In addition to the above, many methods, such as a production method of silica particles utilizing the alkoxide method, etc. have been proposed (for example, Patent Documents 4 to 10).
Further, Patent Document 11 discloses a production method of a silica sol in which elongate-shaped amorphous silica particles are dispersed in a liquid dispersion. This method comprises hydrolyzing tetraethyl silicate and an ethyl silicate oligomer with an acid catalyst; adding an alkali catalyst thereto to adjust the pH to 7 or more; and heating the resulting product to allow it to polymerize.    Patent Document 1: Japanese Unexamined Patent Publication No. 61-158810    Patent Document 2: Japanese Unexamined Patent Publication No. 11-60232    Patent Document 3: WO2004/074180    Patent Document 4: Japanese Unexamined Patent Application Publication No. 2004-91220    Patent Document 5: Japanese Unexamined Patent Application Publication No. 2002-50594    Patent Document 6: Japanese Unexamined Patent Application Publication No. 2005-162533    Patent Document 7: Japanese Unexamined Patent Application Publication No. 2005-60219    Patent Document 8: Japanese Unexamined Patent Application Publication No. 2002-45681    Patent Document 9: Japanese Unexamined Patent Application Publication No. 2005-312197    Patent Document 10: Japanese Unexamined Patent Application Publication No. 2005-60217    Patent Document 11: Japanese Unexamined Patent Application Publication No. 2001-48520